1. Field of the Invention
The present invention relates to a sealing mechanism for sealing a vacuum chamber, and more particularly to a sealing mechanism for sealing a vacuum chamber formed in the semiconductor producing apparatus to be shut down from its exterior.
2. Description of the Related Art
In general, the semiconductor producing apparatus of this kind is maintained vacuumized and highly pure in air for producing such products because dusts and other foreign materials are detrimental to wafers and other semiconductor materials in the process of producing the semiconductor producing apparatus. The semiconductor producing apparatus is usually required to be operated by some kinds of driving mechanism such as a manipulator driven by a drive shaft to handle semiconductor devices, LCD base plates and other objects to be treated. The drive shaft has axial portions extending inside and outside of a vacuum chamber formed in the semiconductor producing apparatus. This means that the gaps between the axial portions of the drive shaft and the other parts around the axial portions of the drive shaft are required to be tightly sealed to have the vacuum chamber maintained at a constant vacuum level.
In recent years, meanwhile, the process of producing semiconductors has remarkably been progressed to obtain more excellent performance, higher density and integration for the products. The process, however, tends to have a relatively low productivity as compared with other industrial products. This is due to the fact that dusts and foreign materials detrimental to wafers and other semiconductor materials are apt to enter the vacuum chamber of the semiconductor producing apparatus. The dusts and foreign materials which may cause inferior products are each made of a particle generally larger than the thickness of an insulator layer to be turned into a semiconductor. At the present time, strenuous efforts continue to be made for reducing to as a lowest level as possible such dusts and foreign materials each having a size larger than the thickness of the insulator layer. These strenuous efforts have not yet become successful.
The typical conventional semiconductor producing apparatus is partly shown in FIG. 15 and comprises a manipulator 210 drivably installed in the vacuum chamber 261 of the semiconductor producing apparatus which is vacuumized through an aperture 201 formed in the wall of the semiconductor producing apparatus.
The manipulator 210 is shown in FIG. 16 as having a drive shaft 250 which is rotatably supported on a support member 240. The wall portion 202 of the semiconductor producing apparatus is formed with a hole 202a having the support member 240 fixedly received therein. The drive shaft 250 shown in FIG. 15 has a forward end portion extending in the vacuum chamber 261 to pivotally support first and second robot arms 213 and 214, and a handling member 215 operatively coupled with the first and second robot arms 213 and 214 so that the handling member 215 can be operated to handle semiconductor devices, LCD base plates and other objects to be treated. Also, the drive shaft 250 has a rear end portion extending in the atmosphere 260 and drivably connected with driving means constituted by an electric motor and reduction gears which are not shown in the drawings.
The drive shaft 250 is shown in FIG. 16 as comprising a first cylindrical shaft 230 rotatably received in the support member 240 through bearings 216a and a second cylindrical shaft 220 rotatably received in the first cylindrical shaft 230 through bearings 216b. 
One typical example of the conventional sealing mechanisms is also shown in FIG. 16 to comprise a first group 218 of magnetic fluid seals axially arranged between the support member 240 and the first cylindrical shaft 230, and a second group 219 of magnetic fluid seals axially arranged between the first and second cylindrical shafts 230 and 220. The two groups 218 and 219 of magnetic fluid seals can function to maintain the vacuum chamber 261 in a hermetically sealed state, resulting in the fact that dusts and foreign materials, i.e., fine particles generated from frictional contacts between elements or parts outside of the vacuum chamber 261 can be prevented from entering the vacuum chamber 261.
The conventional sealing mechanism mentioned in the above is of a performance having a resistant pressure of 0.2 atmospheric pressure for each of the magnetic fluid seals 218 and 219. From this reason, the conventional sealing mechanism is required to comprise a plurality of magnetic fluid seals 218 axially disposed in a series between the support member 240 and the first cylindrical shaft 230, and a plurality of magnetic fluid seals 219 also axially disposed in a series between the first and second cylindrical shafts 230 and 220 as described in the above.
The above known sealing mechanism, however, encounters such a problem that the dusts and foreign materials cannot fully be prevented from entering the vacuum chamber and that the vacuum chamber thus cannot be maintained at a constant vacuum level.
It is, therefore, an object of the present invention to provide a sealing mechanism suitable for sealing a vacuum chamber formed in the semiconductor producing apparatus.
It is another object of the present invention to provide a sealing mechanism having an excellent sealing performance to seal a vacuum chamber formed in the semiconductor producing apparatus.